The invention relates to packings between a shaft and housing, and more specifically to a packing arrangement adapted for either linear motion or rotary motion shafts for sealing between the shaft and housing at normal temperature operating conditions and also at abnormally high temperature conditions as might be encountered in an emergency operating condition such as a fire.
Heretofore, there have been a wide variety of packing assemblies and arrangements for providing for sealing between a valve stem and valve body at high temperatures. It is also well known to use two sets of packings separated by a lantern ring or the like which is connectable to an external source of lubricant or other injectible substance to enhance sealing effectiveness. Such an arrangement is shown in U.S. Pat. No. 4,379,557 which incorporates both low temperature and high temperature packing assemblies. High temperature packing assemblies normally require a preload by means of axial compression to effect a seal. It is characteristic of the arrangement, however, that the high temperature packing assembly will lose its energization and sealing effectiveness in the event of a decomposition of the low temperature packing due to the failure of its material for the high temperature packing and resulting loss of axial compression since the fluid pressure from the flowline or other pressure source will rarely act to pressure energize the high temperature packing.
It is an object, therefore, of the present invention to provide a packing arrangement which is reliably effective for sealing between a shaft and housing at normal temperature operating conditions as well as high temperature operating conditions.
It is another object to provide a packing arrangement of low temperature and high temperature packing assemblies which are tandemly disposed in a single packing chamber and which will reliably maintain energization and sealing effectiveness of the high temperature conditions which cause decomposition of the low temperature packings.
It is a further object to provide a packing arrangement of both low temperature and high temperature packing assemblies tandemly disposed in a single packing chamber which is characterized by a stepped dual diameter configuration for housing the low temperature and high temperature packing assemblies in the smaller and larger diameter sections thereof, respectively, and includes a reliable packing support between the two packing assemblies to permit retention of sealing effectiveness of the high temperature packing assembly in the event of a decomposition of the low temperature packing.
The invention is a "fire-resistant" packing arrangement which features a unique stuffing box configuration and packing assembly adapted for sealing around linear motion or rotary motion shafts such as valve stems. The bore through which the shaft or valve stem extends is successively enlarged to provide a "stepped" dual diameter packing chamber for receiving successive stem packings therein. A primary packing structure in the smaller diameter chamber section located nearest the fluid pressure provides for primary sealing under normal temperature and operating conditions. Secondary sealing under abnormally high temperatures and operating conditions is provided by a secondary packing assembly disposed in the chamber section of greater cross-sectional area. A packing support ring located intermediate the two packing assemblies and adapted to be supported on the radial shoulder provided by the enlargement of the valve stem bore permits the secondary packing to remain energized and maintain a seal in the event of a decomposition of the primary packing due to abnormally high temperatures. A radial shoulder formed by the valve stem bore or shaft bore provides an inner packing stop. A packing retainer ring which is threaded into the bore at the other end of the packing arrangement provides an outer packing stop which is axially adjustable to establish initial energization of the packings.